Geneva Stop Work

Geneva Stop Work

The Geneva Stop Work known also as Maltese cross was a major contributor to timekeeping accuracy in both Watches and Clocks. The stop-work mechanism when used with older high carbon steel springs effectively ‘clipped’ or disengaged the end portions of a mainspring where extreme torque variation occurs leaving the middle much more constant torque flat portion of the mainspring to power the gear train.
This simple easy to manufacture design made the Geneva Stop Work an inexpensive, commonly encountered improvement on both watches and clocks.

I tried to show as much as possible using animation so I hope this is helpful for anyone wanting to know more about how the Geneva Stop work works and how to go about setting mainspring pre-tension.

Enjoy!

This video covers:

  • Geneva stop work purpose
  • Theory on why ‘clipping’ the torque off of the ends of the mainspring is important
  • Ratios
  • Setting up mainspring pre-tension

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BobGeneva Stop Work

Comments 2

  1. malcolm idris lewis

    Thank you for your excellent video.
    Please could you explain one thing to me after setting the pretension from the bottom end of the spring that is putting on one turn of preload onto the main spring will this also have the effect of removing the final turn of the mainspring? Or is that done in another way? confused

    1. Post
      Author
      Bob

      Good to hear you liked the video Malcolm!
      Yes you’re correct. In the example I use in the animation, pre-loading one complete turn of the mainspring at the bottom end will automatically clip a turn at the opposite end. When winding the timepiece the convex face will come into play after four complete turns of the winding key/crown. This also applies to loading by backing off one turn from full wind and then setting the stop. The Geneva stop will take care of the opposite end.
      Important to understand is that the mainsprings maximum usable energy and torque is never wound into the barrel. When winding the watch/clock the last turn will be stopped by the convex face allowing only five winding turns (the one pre-load plus the four turns allowed by the Stopwork) to pass into the barrel. Result is use of the flatter portion of the torque curve and less overall tension on the spring when the timepiece is fully wound.

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